Project Summary/Abstract Deaf children are at risk for impoverished and/or delayed exposure to language, spoken or signed. Early vocabulary is a robust predictor of later language development, and understanding the trajectory of vocabulary development in deaf children can help educators and researchers develop interventions to mitigate the risks and effects of language deprivation. Two factors that might play a unique role in sign language vocabulary acquisition are neighborhood density and iconicity. Typically hearing children track statistical information about the sounds of language to acquire new words, and words that sound similar to many other words (have high phonological neighborhood density) are overrepresented in early spoken vocabularies. Sign language phonology is not based on sounds that are sequentially organized but on features like hand configurations and locations that are articulated simultaneously. There is also a dearth of minimal pairs in many sign languages. We ask whether deaf children track statistical information about combinations of manual features as children acquiring spoken language track phonological information about words, or if the nature of sign phonology makes signs more amenable to holistic processing and acquisition. If the former is true, we expect signs with high neighborhood density to be overrepresented in early vocabularies just as in speech acquisition; if the latter is true neighborhood density should not play a role in sign acquisition. The second factor that may play a unique role in sign acquisition is the abundance of iconicity in signed languages. It is unclear whether children can make use of iconic relationships between sign forms and meanings because iconicity is confounded with neighborhood density in sign language. In the proposed study we ask for the first time whether iconicity predicts signed vocabulary acquisition while controlling for neighborhood density and frequency in child-directed speech by using parental reports of children?s ASL vocabulary skills (ASL-CDI). All of the lexical and input factors gathered in this study (expressive and receptive age of acquisition norms, type of iconicity, and frequency in child-directed speech) will be made publically available by integrating with an interactive online database of ASL vocabulary, ASL-LEX. ASL-LEX currently contains information about neighborhood density, degree of iconicity, lexical class, and frequency in adult-directed speech, as well as several other properties. This work will shed light on the factors that shape vocabulary acquisition in native signing children, and will lay the groundwork for understanding vocabulary development in deaf children of hearing parents acquiring sign language later in development.